Devices for firing a projectile

ABSTRACT

A housing ( 1; 100, 104, 102 ) of a cartridge for a device for firing a projectile has separate first and second chambers ( 10, 12; 106, 114 ), each of which contains a respective charge ( 34, 36; 108, 110, 116, 120 ) of propellant material. Gas produced by the detonation of one of the charges exits the first chamber to propel the projectile, whilst gas from the detonation of the second charge exist rearwardly from the device so as to counteract recoil. A one way valve may also be provided to help to achieve a high pressure difference between the chambers, where the cartridge has a common igniter assembly.

FIELD OF THE INVENTION

This invention relates to a cartridge for a device for firing a projectile and to a device for firing a projectile. Although described in relation to a device for de-arming/disrupting an explosive device, the invention is not limited in application to de-arming and disrupting devices.

BACKGROUND TO THE INVENTION

A conventional de-arming device (also referred to as a disrupting device or a de-armer disrupter) operates by firing a solid, liquid or gel projectile at an explosive device so as to disrupt the fuse assembly of the latter, ideally without detonating the explosive device. Such a de-arming device comprises a barrel, the breech of which contains a conventional gun cartridge which, when detonated, propels the projectile, also initially contained in the barrel, towards the target.

It is generally desirable to provide means for reducing the recoil caused by the firing of the projectile, and to that end it is known to fit the end of the barrel with rearward facing venturi ports through which some of the gas caused by the detonation of the cartridge passes. However, these ports reduce the pressure of the gases which are used to propel the projectile, and thus result in the device requiring a relatively large charge and long barrel in order to be able to accelerate the projectile to a sufficiently high velocity.

It has also been proposed to deal with the problem of recoil by fitting the de-arming device with a retro-active rocket taking the form of a second cartridge housed in a second barrel breech opposed to the first barrel. The second gun cartridge is fired simultaneously with the first cartridge so that the recoil caused by firing the first cartridge is counteracted by that caused by the firing of the second cartridge.

Although the anti-recoil system of such device does not require a longer primary barrel (for the projectile), the additional barrel breech does increase the size and weight of the device. Furthermore, the device can take a relatively long time to be primed for firing and it can be difficult to detonate both cartridges simultaneously.

The present applicant's European Patent No. EP0549659B discloses a de-arming device in which recoil is counteracted by means of water initially contained in an annular chamber around the breech of the barrel. The gun cartridge used to fire the projectile also propels the water rearwardly from the device. The inertia of the water enables the gun cartridge to generate sufficiently high gas pressures to fire the projectile at a sufficiently high velocity without the need to lengthen the device's barrel. However, the water and the additional components needed for the firing device to contain the water increase the weight of the device, and the need to fill the chamber with water prior to firing the device (and to close the chamber once full) also increases the time needed to prime the device for firing.

Over recent years, small robotic vehicles, weighing in the region of 30 kilograms, have increasingly been deployed to carry out remote reconnaisance work and to carry a de-armer which can be remotely fired. One example of such a device is the pakbot mini rov produced by iRobot. Such vehicles are able to carry recoilless de-armers such as the de-armer shown in EP0549659 on their lower or middle arms. There is an increasing need for the vehicles to be provided with recoilless de-armers on their upper arms in order for the vehicle to be able to de-arm or disrupt targets in, for example, overhead luggage lockers on aircraft, trains, buses and in other high reach situations. However, the upper arm of such a vehicle would not be able to carry a de-armer which weighs more than 1.5 kilograms whereas the various designs discussed above generally weigh at least 3 kilograms.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a cartridge for a device for firing a projectile, the cartridge comprising a housing having first and second chambers, respectively containing first and second charges of propellant material, and each having a respective outlet, wherein, in use, the outlet of the first chamber allows the expulsion from the cartridge of gas produced by the detonation of the first propellant charge, so as to fire the projectile, whilst the outlet of the second chamber allows the expulsion from the cartridge of gas produced by the detonation of tie second propellant charge, which gas exits the device rearwardly so as to counteract recoil.

Since the two charges of propellant, one for firing the projectile, the other for counteracting recoil, are contained in a common cartridge, a device which fires a projectile using that cartridge can have a single breech, and can therefore be more compact and lightweight than a device which uses two separate cartridges. The device is also more compact and lightweight than types of anti-recoil de-armer that do require a jacket of water. Since the propellant charge for firing the projectile is in a separate chamber from that for counteracting recoil, the force with which the projectile is fired is not affected by the gases by which are ejected so as to counteract recoil. Accordingly, the amount of the first propellant charge can be varied independently of the second propellant charge during the stages of design and development of the cartridge. This facilitates the creation of a cartridge which provides a desired force of firing and adequate anti-recoil characteristics. Indeed, it has been found that a cartridge in accordance with the invention can completely neutralise recoil.

Preferably, the chambers of the cartridge are situated one in front of the other in the housing, the first chamber being in the front portion of the cartridge, the second in the rear.

Thus, each chamber is situated adjacent to the part of the device (the barrel containing the projectile or a rearward facing outlet port (as the case may be) to which gases from the chamber need to be expelled. In this case, the outlet of the first chamber made to advantage comprise a port in the front of the cartridge, the outlet of the second chamber comprising a port in the rear of the cartridge.

Preferably, the ports are substantially circular, and are coaxial.

Preferably, the chambers are elongate and are also coaxial with the ports and hence with each other.

This facilitates the balancing of the device so that the force generated by the rearwardly ejected gases is coaxial with the recoil force caused by the firing of the projectile.

Preferably, the second charge of propellant is more powerful than the first charge.

This could be achieved by having a more powerful formulation of charge, but is preferably achieved by an arrangement in which the second charge is bigger than the first charge.

The reaction forces on the device caused by the exiting projectile are higher than the reaction caused by ejecting gas alone. This is accommodated in the cartridge by increasing the amount and/or velocity of the gases ejected through the outlet of the second chamber compared with those ejected by the detonation of the first charge.

The second chamber may therefore to advantage be of a larger volume than the first chamber.

Conveniently, the second chamber has a larger cross-sectional area than the first chamber. Thus, if the chambers are cylindrical, the second chamber preferably has a larger diameter than the first chamber.

Consequently, the increased volume of the second chamber does not require an increased length of cartridge.

Preferably, the propellant material is explosive.

Preferably, the two chambers have a common igniter assembly.

This helps to ensure that the detonation of the two charges of propellant material is synchronised.

The igniter assembly may comprise an ignition chamber having ignition ports to each of the first and second chambers and containing an initiator charge of explosive material, hot gases produced by the detonation of which pass through the ignition ports to ignite the first and second charges of propellant material.

The ignition chamber is preferably interposed between said first and second chambers.

Preferably, the cartridge housing comprises a one piece casing which is hollow to define the first and second chambers, and includes a wall or bulkhead separating those two chambers.

The bulkhead isolates the two propellant charges from each so that the firing force exerted on the projectile by the detonation of the first charge is not affected by the venting of the gases produced by the detonation of the second charge.

The bulkhead may to advantage also contain the igniter assembly.

Preferably, the second chamber has a portion of reduced cross section adjacent to the outlet of that chamber.

This acts as a choke which helps to increase the pressure of gases ejected from the second chamber.

According to a second aspect of the invention, there is provided a device for firing a projectile, the device comprising a barrel for housing the projectile and a cartridge in accordance with the first aspect of the invention, wherein the barrel has a rear outlet through which said gas from the detonation of the second propulsive charge of such a cartridge is expelled so as to counteract recoil.

Preferably, the barrel has a breech module, the rear portion of which is of a larger cross sectional or area than the front portion.

Consequently, the rear portion of the breech can accommodate the part of the cartridge which in turn contains the second, larger propellant charge.

Preferably, the rear outlet is connected to a constriction, preferably a venturi, for accelerating the flow of gas from the rear of the device.

The invention also lies in a device in accordance with the second aspect of the invention when loaded with a cartridge in accordance with the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: —

FIG. 1 is a sectional side view of a first embodiment cartridge in accordance with the invention;

FIG. 2 is a corresponding view of a device, also in accordance with the invention, for firing a projectile, the device being shown when loaded with the cartridge shown in FIG. 1;

FIGS. 3 and 4 are isometric views, respectfully from the front and rear, showing the exterior of the device;

FIG. 5 is a sectional side view of a second embodiment of cartridge in accordance with the invention;

FIG. 6 is an end view of the cartridge of FIG. 5 and

FIG. 7 is an isometric view of the cartridge of FIG. 5.

DETAILED DESCRIPTION

The cartridge shown in FIG. 1, comprises a one piece cylindrical housing 1 machined from solid stainless steel, and having a front portion 2 and a rear portion 4 of a larger diameter than the portion 2. On the exterior of the casing, the portions 2 and 4 meet at an annular step 6. At the region of the shoulder 6 the casing includes internal bulkhead 8 which extends across the entire width of the casing to separate the interior of the latter into a first chamber 10 in the front of the cartridge and a second, larger diameter chamber 12 in the rear portion 4.

A further, ignition chamber 14 is provided in the centre of the bulkhead 8, in order to house an igniter assembly.

In this particular case, the igniter assembly includes an electrical fusehead shown diagrammatically at 16, comprising an electrical bridge wire connected to a positive electrical contact 18 and to the casing of the cartridge (which is in turn connected to an earth contact as described below) and coated with a suitable explosive. The fusehead wire is spaced from the walls of the chamber 14, which chamber is also packed with a charge of black powder that acts as an initiator charge.

One side of the chamber 14 is defined by the part 20 of the bulkhead 8 that separates the chamber 10 from the chamber 14, which part includes a pair of ignition ports in the form of axial passages, 22 and 24. The other side of the chamber 14 is defined by a cylindrical externally screw threaded plug 26 which is screwed into a correspondingly screw threaded cylindrical recess 28 in the side of the bulkhead that bounds the compartment 12. The plug 26 also has a pair of axial passages 30 and 32 which act as ignition ports. As can be seen from FIG. 1, the passages 22, 24, 30 and 32 enable the chamber 14 to communicate with the chambers 10 and 12.

The chamber 10 contains a first propellant charge 34, whilst a second propellant charge 36 is contained within the chamber 12. The propellant charge 36 is larger than the charge 34, in this case the charges being respectively constituted by 5 and 8 grams of gun powder. Each of the charges is held in a substantially cylindrical shape, and the end of each charge opposite the bulkhead is abutted by a respective one of two circular card discs 38 and 40 which separate the charge from a respective one of two felt closure wads 42 and 44. The opposite side of each wad is abutted by a respective one of two tufnell discs 46 and 48 which is held in position by means of a respective one of two roll crimps 50 and 52 on the end of the cartridge. The forward end of the cartridge constitutes a circular opening which is closed by the disc 46 and which acts as an outlet for the chamber 10. The outlet for the chamber 12 is provided by the opening at the rear end of the cartridge, which opening is closed by the disc 48. The wall of the cartridge casing includes an annular thickened portion 54 adjacent to the disc 48. This portion acts as a choke for restricting the flow of gases from the chamber 12 and thus increasing the pressure exerted by those gases.

Referring to FIG. 2, the device for firing a projectile, comprises a barrel having a forward portion 56 and a breech module 58 which, in use, accommodates the cartridge. Prior to firing, the projectile (not shown) is accommodated in the forward portion 56.

The device is annular, and the breech module 58 is stepped, having a forward smaller diameter portion 60 and a rear larger diameter portion 62. The interior of the breech module is correspondingly stepped so that the portion 60 accommodates the portion 2 of the cartridge, whilst the portion 62 accommodates the rear portion 4 of the cartridge and the shoulder 6 abuts an internal, correspondingly annular shoulder formed at the step in diameters of the breech portion. This abutment of the two shoulders limits the forward movement of the cartridge within the breech module. The rear of the breech module 58 includes an internal screw thread via which a correspondingly screw threaded end portion 64 can be removably attached to the breech module 58. The portion 64 is open ended, annular and includes a venturi port 66 through which gases generated by the detonation of the charge 36 are expelled from the rear of the device.

As can be seen from FIGS. 3 and 4, the end piece includes a flat 68 to enable the end piece to be rotationally keyed to a suitable tool for tightening and loosening the end piece.

The device is primed for firing by removing the end piece 64 and inserting a cartridge into the breech portion 58 until the shoulder 6 abuts the corresponding shoulder on the interior of the breech portion 58. The end piece 64 is then screwed onto the rear of the breech module 58 and tightened using a tool (as mentioned above). A projectile to be fired from the device is loaded into the device through the front of the barrel 56 until the trailing end of the projectile abuts the front of the breech portion 58. In this particular case, the projectile is a solid, but the projectile could be a liquid or gel (in which case containment of the projectile prior to firing is achieved in the same way as with a conventional projectile of that type).

The breech module 58 carries a pair of terminals, one of which, the terminal 70, is in electrical contact with the contact 18. The other terminal, referenced 72, is in contact with the body of the breech module, and hence is in electrical contact with the casing of the cartridge. Accordingly, the contact 70 comprises a conductive pin 74 which extends through an insulating sleeve 76 that lines the interior of a radial passage in the breech module 58 in registry with the contact 18.

An electrical firing circuit (not shown) is connected to the device by connecting the positive terminal of the circuit to the terminal 70 and the negative terminal of the circuit to the terminal 72.

In response to a suitable firing command, the circuit passes an electrical current through the fuse head wire 16. This detonates the charge of explosive in the chamber 14, causing hot gases to pass through the passages 22, 24, 30 and 32 into the propellant charges 34 and 36, both of which are thus ignited. Since both charges 34 and 36 are ignited from a common fuse wire, the detonation of the two charges occurs substantially simultaneously. This would not necessarily be the case if two separate fuse wires were used since, in general, the resistances of fuse wires (even of the same type) tend to vary so that two such fuse wires will take different amounts of time to heat up to ignition temperatures even if they are subjected to the same voltage simultaneously.

The detonation of the charge 34 shatters the disc 46, ejects the wad 42 and disc 38 and propels the projectile through the front of the barrel 56. As this happens, the bulkhead 8 provides a reaction surface via which the reaction to the force exerted on the projectile by the explosive charge is transmitted into the device. The detonation of the charge 36 causes the disc 48 to disintegrate, and ejects the wad 44 and disc 48 through the venturi 66. As this happens, the wad 44 will fleetingly block the venturi 66 which causes a further build up of pressure of gases generated by the charge 36.

Once the wad 44 and disc (or remnants thereof) 40 have cleared the venturi port 66, gases are ejected through the rear of the device, and the reaction to this is transmitted, via the bulkhead 8 to the rest of the device so as to counteract the recoil caused by the firing of the projectile.

It has been found that a device such as the one described can be made to a weight of approximately one-third of the current designs (which utilise water jackets to counteract recoil), and can therefore be deployed on the upper arm of a mini ROV. The device is also shorter and significantly smaller in diameter than the aforesaid known device, which also make it easier to deploy on an ROV. Furthermore, collateral danger to the rear of the device significantly lower since only gas, rather than water, is ejected. This means that positioning of the system on a robotic vehicle is less critical than in the case of known designs which use water jackets and which therefore require a clear field behind the device to avoid damage to cameras, cables, connectors and antennas. The device according to the invention is also simple to manufacture and easy to operate and maintain.

Turning to FIG. 5 to 7, the second embodiment of the cartridge in accordance with the invention has a three part housing formed from two cupped aluminium end pieces 100 and 102 attached one to either side of a central, cylindrical, stainless steel connector 104.

The cupped piece 102 defines a chamber 106 which contains two propellant charge portions 108 and 110 which correspond to the first propellant charge 34 of the first embodiment. The charge portion 110 is of a relatively slow burning explosive propellant material, whilst the charge portion 108 is of a faster burning explosive material. The two charge portions are separated by a paper disc 112. Similarly, the cupped end piece 100 defines a chamber 114 in which are contained a charge portion 116 of slow burning explosive propellant separated by a paper disc 118 from a charge portion 120 of fast burning explosive propellant. The charge portions 120 and 116 correspond to the second propellant charge 36 of the first embodiment. As can be seen from FIG. 5, each of the slow burn charge portions 110 and 116 is interposed between the connector 104 and a respective one of faster burn charge portions 108 and 120.

Each of the aluminium end pieces 100 and 102 has a closed end, respectively referenced 122 and 124 which, on firing of the cartridge, bursts open to provide an outlet for the respective chamber. In order to facilitate this change, the end 122 is scored with a generally star-shaped burst pattern 126. A similar pattern 128 is scored into the end of the cupped piece 102.

The charge portion 110 is constituted by 7.5 grams of SP12, whilst the charge portion 108 is constituted by 4 grams of OBP473-31 (also known long shot). The charge portion 116 is constituted by 3 grams of SP13 and the charge portion 120 by 7.5 grams of long shot.

The end of the piece 102 opposite the closed end 124 is provided with an internal screw thread at 130 via which the piece 102 is screwed onto a correspondingly externally screw threaded collar portion 132 of the connector 104. A similar screw threaded connection is provided between the connector 104 and the end piece 100 as shown at 137. A central radial flange 135 of the connector 104 provides a stop against which the inboard ends of the pieces 100 and 102 abut.

The collar 132 also has an internal screw thread 134 via which an externally screw threaded stainless steel plug 136 is attached to the connector 104 to define a bulkhead for the chamber 106. An eccentric axial bore 138 connects the chamber 106 to an ignition chamber 140, which contains an electrical fuse head 142 (similar to the fuse head 16 of the first embodiment). As with the fuse head 16, one side of the fuse head wire is connected to a positive electrical contact 144, the other to earth, and an axial brass ferrule 146 lines the ignition chamber 140.

The side of the chamber 140 opposite to the plug 136 is provided with a short passage 148 which is concentric with the connector 104, and which leads a dished seat portion 150. The seat portion leads to a small, generally cylindrical gallery 152 which accommodates a valve member 154 comprising a steel ball. The gallery 150 is formed in a stainless steel, axial plug 156 which is provided with a central axial bore 158 situated between two diametrically opposed 1.2 nm bores 160. The plug, along with the adjacent face of connector 104, provides a bulkhead for the chamber 114.

The plug 156 carries an external screw thread which co-operates with an internal screw thread in the portion of the connector 104 in which the plug 156 is accommodated so as to retain the plug 156 in position.

The operation of the igniter assembly results in hot gases from the burning black powder in the chamber 140 passing through the bore 138 to ignite the propellant charge portion 110, and thus causes subsequent ignition of the portion 108. The detonation of these two portions provides the propulsive force for the projectile (for example a slug of water) to be fired from the device. Because of the mass of projectile, it has been found that less pressure is needed to impart the desired momentum to the projectile than is required to counteract the recoil of firing the projectile. Accordingly, the detonation of the charge portions 120 and 116 generates higher gas pressure than the detonation of the portions 110 and 108. In order to prevent the gas pressures on both sides of the connector 104 tending to equalise through the effect of the chambers 114 and 106 communicating through passages in the connector 104 and the plugs 136 and 156, the valve member 154 and the seat 150 act as a poppet valve.

More specifically, hot gases from the burning black power in the ignition chamber 140 pass through the bore 148 and unseat the ball 154, driving the latter against the passage 158. However, the passages 160 remain clear of the ball so that the gases can still flow through the gallery 152, into the passages 160 and hence into the chamber 114 where they ignite the charge portion 116 and (subsequently) the charge portion 120.

The ignition of the two charge portions causes a large increase of pressure in the chamber 114, and this acts, through the passage 158, on the ball 154, forcing the latter back against its seat 150, and thus closing the passage 148. Consequently, those gases are prevented from reaching the chamber 140, the chambers 106 and 114 thus being sealed from each other. Accordingly, the second embodiment of cartridge can be configured to provide a relatively high differential of pressure between the gases exiting its opposite ends. 

1. A cartridge for a device for firing a projectile, the cartridge comprising a housing having first and second chambers, respectively containing first and second charges of propellant material, and each having, when the cartridge is fired, a respective outlet, wherein, in use, the outlet of the first chamber allows the expulsion from the cartridge of gas produced by the detonation of the first propellant charge, so as to fire the projectile, whilst the outlet of the second chamber allows the expulsion from the cartridge of gas produced by the detonation of the second propellant charge, which gas exits the device rearwardly so as to counteract recoil.
 2. A cartridge according to claim 1, in which the chambers of the cartridge are situated one in front of the other in the housing, the first chamber being in the front portion of the cartridge, the second in the rear.
 3. A cartridge according to claim 2, in which the outlet of the first chamber comprises a port in the front of the cartridge, the outlet of the second chamber comprising a port in the rear of the cartridge.
 4. A cartridge according to claim 3, in which the ports are substantially circular, and are coaxial.
 5. A cartridge according to claim 1 in which the chambers are cylindrical and are coaxial with each other.
 6. A cartridge according to claim 1, in which the second charge of propellant is more powerful than the first charge.
 7. A cartridge according to claim 1, in which the second chamber is of a larger volume than the first chamber.
 8. A cartridge according to claim 7, in which the second chamber has a larger cross-sectional area than the first chamber.
 9. A cartridge according to claim 1, in which the propellant material is explosive.
 10. A cartridge according to claim 1, in which the two chambers have a common igniter assembly for detonating the propellant charges.
 11. A cartridge according to claim 10, in which the igniter assembly comprises an ignition chamber having ignition ports to each of the first and second chambers and containing an initiator charge of explosive material, hot gases produced by the detonation of which pass through the ignition ports to ignite the first and second charges of propellant material.
 12. A cartridge according to claim 11, in which the ignition chamber is interposed between said first and second chambers.
 13. A cartridge according to claim 1, in which the cartridge housing includes at least one wall or bulkhead separating the two chambers.
 14. A cartridge according to claim 13, in which the bulkhead also contains the igniter assembly.
 15. A cartridge according to claim 1, in which the second chamber has a portion of reduced cross section adjacent to the outlet of that chamber, the portion acting as a choke which helps to increase the pressure of gases ejected from the second chamber.
 16. A device for firing a projectile, the device comprising a barrel for housing the projectile and for housing a cartridge in accordance with claim 1, wherein the barrel has a rear outlet through which said gas from the detonation of the second propulsive charge of such a cartridge is expelled so as to counteract recoil.
 17. A device according to claim 16, in which the barrel has a breech module, the rear portion of which is of a larger cross sectional or area than the front portion.
 18. A device according to claim 16, in which the rear outlet is connected to a constriction for accelerating the flow of gas from the rear of the device.
 19. A device according to claim 18, in which the constriction is a venturi.
 20. A device in accordance with claim 16 when loaded with the cartridge.
 21. A cartridge according to claim 2, in which the cartridge includes a one way valve arranged to allow gases from the igniter assembly to reach, and ignite, the second charge, but subsequently to prevent gases flowing back from the second charge into the first chamber.
 22. A cartridge according to claim 21, in which the valve is situated between the igniter assembly and the second chamber and prevents gas reaching the first chamber by blocking the flow of gas from the second chamber to the igniter assembly.
 23. A cartridge accordingly to claim 22, in which the valve comprises a ball moveable in a gallery from a position in which it is clear of a passage to the gallery from the igniter assembly and of a passage leading from the gallery to the second chamber into a position in which the ball is urged against a seat to block the first said passage.
 24. A cartridge according to claim 23, in which the valve includes a further passage from the gallery to the second chamber, said further passage being so positioned as to convey gas from the second chamber to the ball to urge the latter against its seat.
 25. A cartridge according to claim 24 in which the further passage, the ball and the passage from the gallery to the igniter assembly are aligned.
 26. A cartridge according to claim 1, in which each charge is constituted by a respective pair of charge portions: a fast burning portion and a slow burning portion interposed between the igniter assembly and the fast burning portion. 